1. Field of the Invention
The present invention relates to a heat exchanger for use as an evaporator or a condenser for an air conditioner circuit, a radiator or a heater core for a vehicle, or other type heat exchanger. The invention further relates to methods for manufacturing header pipes of a heat exchanger and for connecting the header pipes and tubes in the heat exchanger.
2. Description of the Prior Art
FIGS. 1 and 2 show a typical conventional heat exchanger which allows heat to be exchanged between a heat exchange medium (for example, a cooling medium or a brine) flowing in the heat exchanger and air passing through the heat exchanger. Heat exchanger 21, as shown in FIG. 1, includes a pair of header pipes 22 extending in parallel relation to each other, a plurality of tubes 23 disposed between the header pipes and connected to the header pipes at their opposite open end portions, and with a predetermined pitch in the vertical direction, a plurality of radiation fins 24 provided on the sides of the tubes, and a pair of reinforcement members 25 disposed on the top and bottom radiation fins.
Each header pipe 22 is constructed from a welded aluminum pipe. A plurality of connection holes 26 are formed through the periphery of header pipes 22 with a predetermined pitch in the axial direction of the header pipe. The end portion of each tube 23 is inserted into a corresponding connection hole 26 so that the inside of the tube is in fluid communication with the inside of the header pipe 22. Both ends of each header pipe 22 are closed by caps 27. An inlet tube (not shown) for introducing the heat exchange medium into heat exchanger 21 is connected to one of the header pipes 22, and an outlet tube (not shown) for delivering the heat exchange medium out from heat exchanger 21 is connected to the other header pipe.
Each tube 23 is formed as a straight tube which is flattened in the horizontal direction. The end portions of tubes 23 are inserted in connection holes 26 of header pipes 22, and fixed therein by, for example, brazing. Corrugated type radiation fins 24 are fixed on the upper and lower surfaces of each tube 23 by, for example, brazing.
The heat exchanger is manufactured, for example, in the following manner.
Welded pipes, formed as header pipes 22, are prepared. A plurality of connection holes 26, each having substantially the same shape as the peripheral shape of tubes 23, are formed on each welded pipe with a predetermined pitch in the axial direction of the welded pipe. Tubes 23 and radiation fins 24 are then arranged in alternating order with the pitch of the tubes equal to the pitch of holes 26. Both end portions of the arranged tubes 23 are inserted into corresponding connection holes 26 of header pipes 22. Once the components are positioned, the portions to be connected are secured together by, for example, brazing.
The connection holes 26 in such a conventional heat exchanger are formed into the periphery of the welded pipe, formed as header pipe 22, after the welded pipe is made. This practice, due to the shape of the welded pipe, requires the use of a special jig or tool for forming the holes. This operation causes the manufacturing of the header pipe to be expensive. Consequently, it is difficult to produce heat exchangers inexpensively. In addition, since it is generally difficult to form connection holes 26 precisely at predetermined positions on the periphery of a welded pipe having a circular cross section, defects are liable to occur while inserting and connecting tubes 23 into the header pipes 22. For example, since the end portions of tubes 23 are merely inserted into corresponding holes 26 of header pipes 22, tubes 23 may be removed from holes 26 by vibration or impact when the arranged heat exchanger is moved before brazing. Furthermore, the welded pipe is made merely by bending a flat plate in the form of a pipe and welding the side edges of the bent plate to each other. In this construction, the welded portion generally does not have a high strength, particularly against pressure. Therefore, cracks due to a high pressure fluid passing through the header pipes are liable to occur on the welded portion during use of the heat exchanger over a long period of time.